Removal of Mg++ and Ca++ ions from NaCl brine

ABSTRACT

Alkaline earth metal ions, e.g., Mg ++  and/or Ca ++ , are removed from alkali metal brines, e.g., NaCl, by use of a particulate, macroporous, anion exchange resin containing the in-situ reaction product of polymeric, amorphous, hydrous zirconium oxide and a source of PO 4  ions, e.g., H 3  PO 4 .

BACKGROUND OF THE INVENTION

Various alkali metal halide aqueous solutions e.g., NaCl brine, containMg⁺⁺ ions and/or Ca⁺⁺ ions which are considered detrimental if theaqueous solution is intended for use in certain applications, such as inan electrolytic process. There are commercial incentives tosubstantially removing the Mg⁺⁺ and/or Ca⁺⁺.

It is known that hydrous zirconium oxide and other zirconium compounds,such as zirconium phosphates, are useful as inorganic ion exchangers.

SUMMARY OF THE INVENTION

An amorphous polymeric zirconium hydrous oxide is formed within theresin beads of a macroporous anion exchange resin, then treated with PO₄to form ZrO(xPO₄), thereby forming novel ion exchange compositestructures which are useful in removing alkaline earths (Mg⁺⁺ and/orCa⁺⁺) ions from alkali metal halide brines.

DETAILED DESCRIPTION

It is known that zirconium hydroxide is prepared by alkali precipitationof an aqueous solution of a zirconyl salt. For the present invention itis preferred that the alkali be ammonia since it is more easily washedout than the alkali metal hydroxides or alkaline earth metal hydroxides.Precipitation at cold (ambient) temperature gives a gelatinous productwhich is substantially Zr(OH)₄ containing about 26.5% water or more. Apartially dehydrated zirconyl hydroxide, ZrO(OH)₂, results from dryingit at elevated temperature (e.g., 100° C.), or from hot-precipitation(e.g., 85° C.) followed by hot drying.

Thus, in the present invention the expression "hydrous zirconium oxide"has within the purview of its meaning any of the various amorphoushydrated forms of zirconium oxide which are substantially or largelyinsoluble in water.

The macroporous anion exchange resin is one which contains anionfunctionality groups. Such resins are available commercially, such aspolymers of styrene crosslinked with divinylbenzene having amine groupsattached thereto. For instance a macroporous anion exchange resin withtertiary amine groups affixed to a styrene-divinylbenzene resinstructure is sold by The Dow Chemical Company under the tradename DOWEXMWA-1. It is within the purview of the present invention to use anymacroporous anion exchange resin.

In general, the polymeric zirconium hydrous oxide is formed within theresin beads by wetting the resin with an aqueous solution of a solublezirconium or zirconyl compound, such as ZrOCl₂.8H₂ O. If excessivezirconium or zirconyl solution is present, it should be drained off andthe resin substantially dried, such as by air-drying. The dried resin,containing the zirconium or zirconyl compound is alkalized orneutralized, preferably by use of NH₄ OH, thereby forming polymericZrO(OH)₂. Excess NH₄ OH and NH₄ Cl (which forms) is washed out, such asby repeated contact with water or NaCl brine. The composite is acidifiedwith H₃ PO₄ thereby forming ZrO(xPO₄), where x is about 0.2 to about 2.

In the general process outlined above, the beginning zirconyl compoundmay be hydrated ZrOCl₂ or the like, such as Zr(NO₃)₄, ZrOBr₂, ZrOI₂, orZr(SO₄)₂, or any such water-soluble zirconium compound which willprecipitate to form ZrO(OH)₂ when contacted with a base, especially NH₄OH. The so-formed ZrO(OH)₂, also called "zirconium hydrous oxide", is anamorphous, polymeric structure. Following the above alkalizing step, thePO₄ used for forming the ZrO(xPO₄) is preferably H₃ PO₄, but may also beany alkali metal acid phosphate, e.g., NaH₂ PO₄ and the like.

Once the ZrO(xPO₄) has been formed, the composite is ready to take onalkaline earth metal values from brine. This is done, for example, byplacing the composite in a vessel, preferably a column, and passingalkaline earth metal-containing NaCl brine through the composite untilthe composite is substantially "loaded" with alkaline earth metal valuesand is ready for another water-washing.

It is within the purview of this invention that the metal salt brine maybe a natural brine, such as seawater or mineral brine, a LiCl brine, aKCl brine, or an alkali metal salt brine which comes from an oredressing, ore leaching, mineral dressing, and the like. The presentnovel composite exhibits a high affinity for, and a strong preferencefor, Mg⁺⁺ and/or Ca⁺⁺ ions. It is also useful as chromatographic packingfor Ca⁺⁺, Mg⁺⁺ analysis.

The product is preferably an amorphous polymeric hydrous zirconium oxideformed within the resin beads of a macroporous anion exchange resinhaving ionizable anion groups, such as tertiary amine groups, whereinthe hydrous oxide is at least partially neutralized (reacted) with PO₄,such as H₃ PO₄. The resin is effective for exchanging alkaline earthmetal ions (especially Mg⁺⁺ and/or Ca⁺⁺) from NaCl brine at alkaline pH.

It is preferred that maximum loading of the hydrous oxide into the resinbe attained, or at least approached. The upper limits are those imposedby the amount of zirconium compound which the resin can imbibe; likewisefor the phosphorous to zirconium ratio. It should be noted thatmacroporous resin is expected to imbibe much more of the zirconium andphosphorous compounds than a gel-type resin.

Using commercially available macroporous resin, a resin compositecontaining about 1.47 moles of Zr/cc is readily obtained as per Example1 which follows; a phosphorous/zirconium ratio of 0.297 in this resin isobtained and is operable.

Theoretically the P/Zr ratio in crystalline zirconyl phosphate could beas high as 2/1, but in practice is difficult to approach. However, themaximum P/Zr ratio which one might expect to prepare from amorphouspolymeric hydrous zirconium oxide is believed to be about 1.6/1.Operability is attained throughout the ranges preferred in accordancewith the present invention, but since the capacity for Ca⁺⁺ and/or Mg⁺⁺are directly related to the P content, then the highest practical P/Zrratio is preferred.

An important operating variable, in using the present composite toremove alkaline earth metal values from an alkali metal brine, is the pHof the brine. this ZrO(xPO₄)-containing resin composition is stable toacidic solutions, e.g., 1N HCl, in contrast to the hydrous Zr oxideresin composition. At a caustic concentration above about 0.1N the Zr/Pis partially soluble. The pH of the brine, as measured by glasselectrode, is preferably in the range of about 5 to about 8.5. The Ca⁺⁺and/or Mg⁺⁺ is best stripped by flowing 1N acid through the column,followed by 0.1 N acid. Regeneration to alkaline pH is best accomplishedby batch treatment with alkali to pH 11, but avoiding pH substantiallyabove 11. For column operation, treatment of the resin with caustic of0.1 N or less is recommended.

A flow rate of about 0.01-0.08 bed volume per minute at about 50°-60° C.is preferred for the brine, though flow rates in the range of 0.001 to0.2 bed volumes per minute at temperatures from about 20°-100° C. areoperable.

By use of the present invention, greater than 99% of the Ca⁺⁺ and/orMg⁺⁺ are removed from 15 bed volumes of 26% brine containing about 0.7gm. Ca⁺⁺ and/or Mg⁺⁺ per liter.

The following example is intended to illustrate an embodiment of thepresent invention, but the invention is not limited to the particularembodiment shown.

EXAMPLE 1

Here, there is used a macroporous anion exchange resin with tertiaryamine groups affixed to a styrene-divinylbenzene resin structure. Theresin is in the amine chloride salt form and is a commercial resin soldby The Dow Chemical Company under the tradename of DOWEX MWA-1-Cl⁻.About 34 gms of this resin is wetted with a solution of about 30 gmsZrOCl₂.4H₂ O in 40 gms H₂ O. The resin absorbed all the solution andbecame free-flowing. The air-dried resin is added to solution of 30 mlof 30% aqueous NH₃ and 10 ml H₂ O. The temperature rose to 40° C. Theexcess NH₄ OH, external Zr(OH)₄ and the NH₄ Cl (which formed) are washedout by repeated contact with excess water. The washed resin was added to40 gm. of conc. H₃ PO₄ in 100 gm H₂ O(pH=1.0), then added 21 gm ofCaCl₂.2H₂ O and neutralized with 30% NH₃ with warming. With 40 ml of 30%NH₃ added, the pH=7.0 at 70° C. The resin was then washed with raw brine(26% NaCl, 681 ppm Ca⁺⁺), the final pH was 6.7 in 26% NaCl by glasselectrode. The product was 115 cc of resin composite. X-ray diffractionanalysis revealed no crystallinity.

The resin prepared was placed with 26% NaCl brine in a temperaturecontrolled jacketed column. Brine was started at 3.3 ml/min. and 75° C.The first 50 cc through was discarded. We then collected 50 cc cuts. NoCa⁺⁺ was found in the brine effluent; the rate was increased to 10cc/min. After 250 cc of brine, there was still no Ca⁺⁺ in effluent.Diluted 15 ml of 36% HCl to 300 ml and pumped through at 10 ml/min.Noted high strength CaCl₂ effluent, pH 6, still after 300 ml of HClsolution. Then followed with 0.1N HCl at 10 ml/min.; acid broke throughafter 50 ml. For 100 ml effluent, pH 1.7, there was very high Ca⁺⁺.After 1000 ml of 0.1N HCl, we switched flow to 0.1N NaOH at 21 cc/min.After 300 ml, effluent pH 1.3 contained no Ca⁺⁺. The 0.1N NaOH wascontinued for 1000 ml, at which time the effluent pH was 3; then flow of200 ml of H₂ O, and back to brine. After 1450 ml a 50 ml sample, pH 1.3,had some Ca⁺⁺.

At this point the resin was removed from the column, suspended intreated (i.e., low Ca⁺⁺) brine, neutralized to pH 8 with caustic thenreturned to the column. A 4% volume decrease in the resin had occurred.Some 600 ml of raw brine containing 681 ppm Ca⁺⁺ +Mg⁺⁺ was passedthrough before Ca⁺⁺ started to increase above 7 ppm.

A third regeneration of the resin was carried out by passing 225 ml 1NHCl at 10 ml/min., then 150 ml 0.1N HCl through the resin in the column.The resin was then removed and batch neutralized with caustic to pH 11.The regenerated resin was then returned to the column and raw brine(i.e., 26% NaCl with 681 ppm Ca⁺⁺) was pumped through at 50° C. and 10ml/min. The following table illustrates the data obtained and confirmsthat the conditions of the last regeneration are the preferredconditions.

                  TABLE I                                                         ______________________________________                                        Volume      pH of    ppm Ca + Mg                                              Out         Effluent (Versene Titration)                                      ______________________________________                                         100 ml     8        0                                                         250 ml     7        0                                                         400 ml     7        0                                                         600 ml     6.5      0                                                         800 ml     6        0                                                        1100 ml     6        0                                                        1300 ml     6        0                                                        1450 ml     6        1                                                        1650 ml     6        8.8                                                      ______________________________________                                    

We claim:
 1. Particulate macroporous anion exchange resin compositeshaving post-deposited therein the in-situ reaction product of polymericamorphous hydrous zirconium oxide and a source of PO₄ ions.
 2. Thecomposite of claim 1 wherein the source of PO₄ ions comprises H₃ PO₄. 3.The composite of claim 1 wherein the macroporous anion exchange resincomprises a particulate water-insoluble polymer having functional aminegroups attached thereto.
 4. The composite of claim 1 wherein the resincomprises a macroporous, particulate polymer of styrene crosslinked withdivinylbenzene and having tertiary amine groups attached thereto.
 5. Amethod for preparing macroporous anion exchange resin particles havingzirconyl phosphate contained therein, said method comprisingimbibing anaqueous solution of a soluble zirconium salt into said particles,alkalizing the zirconium salt to polymeric hydrous zirconium oxide byreaction with an aqueous alkalizer, and converting the so-formed hydrouszirconium oxide to zirconyl phosphate by reaction with a source of PO₄ions.
 6. The method of claim 5 wherein the aqueous alkalizer comprisesammonia.
 7. The method of claim 5 wherein the source of PO₄ ionscomprises H₃ PO₄.
 8. The method of claim 5 wherein the anion exchangeresin comprises a particulate, water-insoluble polymer having functionalamine groups attached thereto.
 9. The method of claim 5 wherein theanion exchange resin comprises a macroporous, particulate polymer ofstyrene crosslinked with divinylbenzene and having tertiary amine groupsattached thereto.
 10. A method for substantially removing alkaline earthmetal ions from alkali metal salt brine, said methodcomprisingcontacting said brine with a particulate, macroporous, anionexchange resin composite containing port-deposited therein the in-situreaction product of polymeric amorphous hydrous zirconium oxide and asource of PO₄ ions.
 11. The method of claim 10 wherein the alkalineearth metal ions comprise Mg⁺⁺ and/or Ca⁺⁺.
 12. The method of claim 10wherein the alkali metal salt brine comprises aqueous NaCl.
 13. Themethod of claim 10 wherein the resin of the composite comprises an anionexchange resin of styrene crosslinked with divinylbenzene and havingamine groups attached thereto.
 14. The method of claim 10 wherein thesource of PO₄ ions comprises H₃ PO₄.
 15. The method of claim 10 whereinthe resin of the composite comprises a particulate, macroporous polymerof styrene crosslinked with divinylbenzene and having tertiary aminegroups attached thereto.
 16. The method of claim 10 wherein the pH ofthe brine is in the range of about 5 to about 8.5.
 17. The method ofclaim 10, using a brine having a temperature in the range of about 20°C. to about 100° C.
 18. The method of claim 10, using a brine having atemperature in the range of about 50° C. to about 60° C.
 19. The methodof claim 10 wherein the contacting of the brine with the resin compositeis performed in a column containing 1 bed volume of the resin and wherethe brine is flowed through the bed at the rate of about 0.001 to about0.2 bed volumes per minute.
 20. The method of claim 19 wherein the flowrate of the brine through the bed is about 0.01 to about 0.08 bedvolumes per minute.